Four of those taken to hospitals needed assistance breathing and were intubated, and a “couple” of others experienced seizures, the Tribune reported, quoting Joe Formhals, the fire chief of the suburb of Joliet.

“I am concerned about it, no question,” Joliet Mayor Tom Giarrante told the newspaper. The mayor raised the possibility of halting the raves in the future if safety problems persist.

“You have to be concerned about it when you’ve got young people like that doing drugs,” the mayor said.

Meanwhile, Michigan State Police reported the death of a 21-year-old man, Joseph Bud Norris, on the first day of the four-day Electric Forest Festival near Rothbury, Mich., about 130 miles northeast of Chicago.

Norris’ June 27 death is being investigated by the local medical examiner, who has not released a cause of death. Organizers of the Electric Forest Festival, coproduced by Insomniac and Colorado-based Madison House Inc., released a statement saying Norris was a subcontractor working on the show.

Michigan State Police Lt. Kevin Leavitt said investigators do not suspect foul play.

A year ago, a 37-year-old man was found dead at his concert campsite at the Electric Forest event. The coroner concluded the cause of death was heart inflammation and drug toxicity.

Insomniac’s chief executive officer, Pasquale Rotella, is under indictment on bribery and other charges in connection with raves at the Los Angeles Memorial Coliseum and adjoining Sports Arena.

Los Angeles County prosecutors allege that he and another rave promoter, Reza Gerami, conspired to keep a lid on concert costs, such as expenses for security, by making about $2 million in illicit payments to a stadium manager. They have pleaded not guilty.

Insomniac spokeswoman Jennifer Forkish said her company’s “top priority at every event is fan safety and security.”

“We look forward to continuing conversations with Joliet officials to examine ways we can make the festival even better next year,” Forkish said.

Forkish earlier told the Tribune that its festival in the Chicago area “did not present any issues that were extraordinary for an event of its size.”

The Joliet fire chief, however, said, his agency took more people to hospitals, and more in critical condition, than it typically does for other events at the Chicagoland Speedway.

In February, The Times reported that since 2006, at least 14 people who attended concerts produced by Rotella and Gerami have died from overdoses or in other drug-related incidents.

Most of the deaths were linked to Ecstasy or similar designer drugs, hallucinogens tightly bound with raves, The Times’ analysis of coroner’s and law enforcement reports from nine states showed.

Forkish said Insomniac has a zero tolerance policy for illegal substances and promotes personal responsibility among its guests.